Which is better to give earthquake early warning: seismometers or GPS?

GPS is recording the actual motion of the ground as it happens, so a warning could be triggered almost instantaneously in a large earthquake and provide valuable seconds for people to prepare. Seismometers, which record seismic waves, require analysis to determine the size and location of an earthquake. This analysis can be done in a few minutes, but those few minutes make a huge difference for those closest to the quake.